There currently is an extensive exploration effort being made in the Arctic regions of the world. It is expected that substantial drilling operations will imminently occur in such areas. Many of these areas are located in offshore areas which are ice covered for extensive periods of time during the year. Some areas are continuously ice covered throughout the year. The ice cover existing in these Arctic areas is subject to massive stresses and strains which result in a variety of configurations ranging from undisturbed sheets to rafted areas and pressure ridges. Certain shallow water areas are covered by land fast ice; i.e., ice sheets which are grounded on the sea floor. In the remainder of the offshore areas, the ice floats on top of the water and is subject to movement by both wind and current. Both the land fast ice and the floating ice are likely to break up and at least partially melt in most areas during the summer months.
Under these conditions it is apparent that conventional offshore platforms used in areas such as the Gulf Coast are fraught with problems of a magnitude which likely eliminates their use in most of the Arctic areas. Since the ice covers most of these offshore areas during the long winter season, it is not practical to use platforms or conventional drilling vessels, since they cannot be moved from one location to another. Ice breakers would be needed to create a sea lane to allow the drilling vessels to proceed to the next location or to allow barges to transport the platforms.
It has been suggested that surface effect vehicles might be used in the Arctic to provide the mobility needed for moving from one location to another. These vehicles have the capability of riding on a cushion of air over land, ice or water and can be constructed to float on water when not hovering. Currently under investigation are surface effect structures which have the capability of carrying all or part of the drilling equipment necessary for drilling exploratory wells. There have been various methods suggested for over ice movement of these structures. In small surface effect vehicles, rear mounted fans can supply sufficient propulsion to move these vehicles at high speeds. However, when surface effect structures are being used of a sufficient size to house drilling equipment, the fan power required for movement is prohibitive. Large tracked vehicles could be used for towing such a surface effect structure. These tracked vehicles tend to be less costly than utilizing a self powered surface effect structure. When it is necessary, however, to move the surface effect vehicles across an open lead in the ice, the tracked vehicles are unusable. These open leads result when tensile forces cause the ice sheet to pull apart, leaving a narrow band of open water. This open water cannot of course be traversed by a tracked vehicle. A suggestion made to obviate the problem of open leads was to tow such large surface effect vehicles by helocopters. This however, is an extremely expensive procedure due to the high amounts of fuel consumed by the helocopters. In view of the foregoing, it is clear that a cheap propulsion system capable of traversing ice sheets and ice leads is desirable for use with surface effect vehicles. It is therefore the object of the present invention to provide a new and improved method and apparatus for moving arctic vehicles in ice covered areas.